Here's some of the main things I don't like about FH:
As previously mentioned, the lack of continuity. There were too many minor recurring characters who just dissapeared with no explanation. Also wish that some of the minor recurring characters were in more episodes in more seasons.
Michelle being a brat in many episodes from season 4 onwards.
The large number of Michelle centred epsiodes, especially in seasons 7 & 8. Also, the large number of episodes involving Michelle's friends.
The season 6 plot where it's revealed that Jesse didn't graduate high school, and then he goes back and finishes it.
The lack of A-plots focussed around DJ & Steph in the later seasons.
The jokes about Danny being extremely cautious (didn't mind him being a neat freak, but the overly cautious thing really got to me.)
Some of the really bad fashions they had on the show.
The overall feel of season 1, with its main focus on the three guys rather than the girls.
When Jesse acts irrationally. For instance, when he pulls Michelle out of preschool, or when he pulls Nicky & Alex out of preschool.